An intracorporeal substance measuring assembly to be provided in an embedded-type substance sensor for detecting and measuring an intercorporeal analyte includes: a detection layer containing at least one fluorescent indicator for generating fluorescence according to the concentration of the analyte; and an optical separation layer which is provided on the detection layer, is optically opaque, permits the analyte to penetrate therethrough, and prevents the penetration therethrough of at least one of living body substances possibly deteriorating the detection layer and/or obstructing the fluorescence.